Generally, electron emission devices are classified into those using hot cathodes as an electron emission source, and those using cold cathodes as the electron emission source. There are several types of cold cathode electron emission devices, including a field emitter array (FEA) type, a metal-insulator-metal (MIM) type, a metal-insulator-semiconductor (MIS) type, and a surface conduction emitter (SCE) type.
The FEA type electron emission device is based on the principle that when a material having a low work function or a high aspect ratio is used as an electron emission source, electrons are easily emitted from the electron emission source when an electric field is applied thereto under the vacuum atmosphere. A sharp-pointed tip structure based on molybdenum Mo or silicon Si, or a carbonaceous material, such as carbon nanotube, graphite and diamond-like carbon, has been developed to be used as an electron emission region.
With the common FEA type electron emission device, cathode electrodes, an insulating layer, and gate electrodes are sequentially formed on a first substrate, and openings are formed at the gate electrodes and the insulating layer. Electron emission regions are formed over the cathode electrodes within the openings. Phosphor layers and an anode electrode are formed on a surface of a second substrate facing the first substrate.
In operation, when scan driving voltages are applied to any one of the cathode and the gate electrodes, and data driving voltages are applied to the other electrode, electric fields are formed around the electron emission regions at the pixels where the voltage difference between the two electrodes exceeds the threshold value. Electrons are emitted from those electron emission regions. The emitted electrons are attracted by the high voltage applied to the anode electrode (a positive voltage of several hundreds to several thousands volts), and collide against the corresponding phosphor layers, thereby light-emitting them.
However, with this type of electron emission device, when electrons are emitted from the electron emission regions, some electrons are non-straightly diffused even though most of the electrons straightly proceed toward the corresponding phosphor layers. The diffused electrons land on the black layers disposed between the phosphor layers, and do not serve to emit the visible rays. Furthermore, the diffused electrons land on incorrect color phosphor layers at the neighboring pixels, and light-emit them so that the image quality is deteriorated.
As the cathode and the gate electrodes have an internal resistance, they may induce voltage drop and signal distortion during the driving of the electron emission device. Particularly when the cathode electrodes are formed with a transparent oxide layer such as indium tin oxide (ITO), they involve higher resistance compared to the case where they are formed with a metallic conductive layer such as aluminum (Al) or silver (Ag).
When the voltage drop and the signal distortion are made, the electric fields applied to the electron emission regions are differentiated per the pixels even when the same driving voltage is applied to all the pixels. As a result, the electron emission uniformity per pixel is deteriorated, and in a serious case, a distinct luminance difference is observed along the length of the cathode or the gate electrodes.